A conventional manually operative steering system of an outboard motor exhibits a significant problem, such as, for example, the fact that the steering load increases, which may result in difficulty in performance of the steering operation, in accordance with navigation conditions, such as, for example, wind or wave conditions, hull speed, trim angle of the outboard motor body and the like.
In order to obviate the problem encountered with the conventional manual steering system, a hydraulic power steering system has been proposed.
The proposed hydraulic power steering system is generally composed of the manual power steering system and a power unit equipped with a hydraulic pump for generating a steering assist force. The power unit applies the steering assist force to the manual power steering system.
However, the hydraulic power steering system described above utilizes the power source of the outboard motor itself as the power source of the hydraulic pump. Accordingly, the steering assist force generated by means of the hydraulic pump is changed in response to the revolutions per minute of the engine, that is, the engine speed, mounted upon the outboard motor, which may not be suitably controlled according to the navigation conditions.